[Numpy-discussion] Scipy dot
njs at pobox.com
Fri Nov 9 10:20:35 EST 2012
On Fri, Nov 9, 2012 at 2:45 PM, Frédéric Bastien <nouiz at nouiz.org> wrote:
> On Fri, Nov 9, 2012 at 3:32 AM, Nathaniel Smith <njs at pobox.com> wrote:
>> On Fri, Nov 9, 2012 at 6:18 AM, Nicolas SCHEFFER
>> <scheffer.nicolas at gmail.com> wrote:
>> > Fred,
>> > Thanks for the advice.
>> > The code will only affect the part in _dotblas.c where gemm is called.
>> > There's tons of check before that make sure both matrices are of ndim 2.
>> > We should check though if we can do these tricks in other parts of the
>> > function.
>> > Otherwise:
>> > - I've built against ATLAS 3.10
>> > - I'm happy to add a couple more test for C and F-contiguous. I'm not
>> > sure how to get the third type (strided), would you have an example?
>> def with_memory_order(a, order):
>> assert order in ("C", "F", "discontig")
>> assert a.ndim == 2
>> if order in ("C", "F"):
>> return np.asarray(a, order=order)
>> buf = np.empty((a.shape * 2, a.shape * 2), dtype=a.dtype)
>> buf[::2, ::2] = a
>> # This returns a view onto every other element of 'buf':
>> result = buf[::2, ::2]
>> assert not result.flags.c_contiguous and not
>> return result
>> > The following test for instance checks integrity against
>> > multiarray.dot, which I believe is default when not compiled with
>> > BLAS.
>> > Dot is a hard function to test imho, so if anybody has ideas on what
>> > kind of test they'd like to see, please let me know.
>> > If that's ok I might now be able to:
>> > - Check for more bugs, I need to dig a bit more in the gemm call, make
>> > sure everything is ok.
>> > - Create an issue on github and link to this discussion
>> > - Make a commit in a seperate branch
>> > - Move forward like that.
>> > ==
>> > import numpy as np
>> > from time import time
>> > from numpy.testing import assert_almost_equal
>> > def test_dot_regression():
>> > """ Test numpy dot by comparing with multiarray dot
>> > """
>> > np.random.seed(7)
>> > a = np.random.randn(3, 3)
>> > b = np.random.randn(3, 2)
>> > c = np.random.randn(2, 3)
>> > _dot = np.core.multiarray.dot
>> > assert_almost_equal(np.dot(a, a), _dot(a, a))
>> > assert_almost_equal(np.dot(b, c), _dot(b, c))
>> > assert_almost_equal(np.dot(b.T, c.T), _dot(b.T, c.T))
>> > assert_almost_equal(np.dot(a.T, a), _dot(a.T, a))
>> > assert_almost_equal(np.dot(a, a.T), _dot(a, a.T))
>> > assert_almost_equal(np.dot(a.T, a.T), _dot(a.T, a.T))
>> You should check that the result is C-contiguous in all cases too.
>> for a_order in ("C", "F", "discontig"):
>> for b_order in ("C", "F", "discontig"):
>> this_a = with_memory_order(a, a_order)
>> this_b = with_memory_order(b, b_order)
>> result = np.dot(this_a, this_b)
>> assert_almost_equal(result, expected)
>> assert result.flags.c_contiguous
>> You could also wrap the above in yet another loop to try a few
>> different combinations of a and b matrices (perhaps after sticking the
>> code into a utility function, like run_dot_tests(a, b, expected), so
>> the indentation doesn't get out of hand ;-)). Then you can easily test
>> some of the edge cases, like Nx1 matrices.
> I agree that tests are needed the for Nx1 and variant cases. I saw blas
> error being raised with some blas version.
> You also need to test with the output provided, so there is 3 loops:
> for a_order in ("C", "F", "discontig", "neg"):
> for b_order in ("C", "F", "discontig", "neg"):
> for c_order in ("C", "F", "discontig", "neg"):
> I also added the stride type "neg", I'm not sure if it is needed, but that
> is other corner cases. neg => result = buf[::-1, ::-1]
> I just looked again at our code and there is another constrain: that the
> strides are multiple of the elemsize. Theano do not support not aligned
> array, but numpy does, so there is a need for test for this. You can make an
> unaligned array like this:
> dtype = "b1,f4"
> a = numpy.empty(1e4, dtype=dtype)['f1']
I think you're mixing up two issues here... requiring that the strides
and the itemsize match is part of the requirement for C- and
F-contiguity, the example code you give here produces a non-contiguous
array, so it's already checked for by the function we're talking
However, there can be contiguous arrays that are not aligned, like:
In : a = np.empty(100, dtype="i1")[1:-3].view(np.float32)
In : a.flags.c_contiguous
In : a.flags.aligned
I suspect the np.dot code that Nicolas is looking at already checks
for the ALIGNED flag and makes a copy if necessary, but it would be
good to have an array like this in the tests to be sure.
> I just saw the strides problems that affect only some. I think that the best
> explaination is our code:
> /* create appropriate strides for malformed matrices that are row or
> * vectors, or empty matrices.
> * In that case, the value of the stride does not really matter, but
> * some versions of BLAS insist that:
> * - they are not smaller than the number of elements in the array,
> * - they are not 0.
> sx_0 = (Nx > 1) ? Sx/type_size : (Nx + 1);
> sx_1 = (Nx > 1) ? Sx/type_size : (Nx + 1);
> sy_0 = (Ny > 1) ? Sy/type_size : (Ny + 1);
> sy_1 = (Ny > 1) ? Sy/type_size : (Ny + 1);
> sz_0 = (Nz > 1) ? Sz/type_size : (Nz + 1);
> sz_1 = (Nz > 1) ? Sz/type_size : (Nz + 1);
> So this ask for test with empty matrices too.
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